Therapeutic Cloning: Will it Work?

What is therapeutic cloning?

Therapeutic cloning is cloning for research purposes.The cloning procedure is called somatic cell nuclear transfer (SCNT).A somatic cell is any cell in the body except the egg or sperm cells, or their precursors.Skin cells, blood cells, brain cells are all somatic cells. Every somatic cell has all of the chromosomes (DNA), unique to each individual, in its nucleus. In SCNT, one takes an egg from a female donor, removes the nucleus, and inserts the somatic cell nucleus with its DNA into the "empty" egg.More simply, SCNT is the transfer of the nucleus from a somatic cell to the egg.The egg is impregnated with all 46 chromosomes of an already existing genome and then "tricked" into thinking it has been fertilized.The fertilized egg begins to divide and a clone is created.In therapeutic cloning, the cloned embryo is then destroyed to harvest cells for research purposes.

Scientists hope that therapeutic cloning will provide embryonic stem cells (ESCs) that are genetically identical to a patient with a degenerative disease. In theory, these tailor-made ESCs can replace damaged cells or tissue that cause conditions such as diabetes, Parkinson's disease, spinal cord injuries, and heart disease.(For more on embryonic stem cells, see the Stem Cell Research topic.)And, unlike ESCs from "leftover" IVF embryos, scientists say that ESCs, created by therapeutic cloning, will be a perfect genetic match to the patient.This would eliminate need for immune suppressive drugs since the ESCs from a cloned embryo would not be rejected.

Michael D. West, chief scientific officer of Advanced Cell Technologies, is a staunch therapeutic cloning supporter.His company, based in Massachusetts, is currently trying to clone human embryos to produce embryonic stem cells.He has high hopes for therapeutic cloning for curing diabetes: "One can imagine the day when doctors swab the inside of the cheek of a patient to get living cells, take them back to an embryonic state by nuclear transfer [cloning], and then steer the differentiation of these primordial cells to create young, healthy beta cells that could be injected back into the body and actually cure this devastating disease."1

What scientists are not telling you

If you listen to many therapeutic cloning advocates like West, they will tell you that therapeutic cloning is the most promising technique to cure degenerative disease.They insist that it is necessary to create and destroy human life to alleviate the suffering of millions of Americans. While therapeutic cloning may result in some useful knowledge, it is not the cure-all that many would like you to believe.

First, a cloned embryo is not an exact genetic match. There is DNA outside of the nucleus in the mitochondria of the egg cell, so the cloned embryo will have some DNA from the egg left in the cell.The cloned embryo will be a hybrid, with DNA from both the cloned individual and the female egg donor.The mitochondrial DNA from the egg donor may have an effect on whether the patient's immune system will reject the stem cells harvested from therapeutic cloning.David Prentice, in his book, Stem Cells and Cloning, writes, "More importantly, for possible transplants, even though there are only 13 genes in human mitochondria, some of the proteins made from these genes do end up on the surface of the cell, where there is the possibility that they could trigger an immune response."2

Second, the much-ignored reality of therapeutic cloning is that, to become a viable commercial therapy, an enormous number of human eggs are required.For every attempt at cloning to harvest embryonic stem cells, it usually requires more than one human egg.In South Korea, it took 242 human eggs to derive one human clone.And then, only 1 in 10 cloned embryos will result in a viable embryonic stem cell line.3So, essentially, it would take close to 2,500 human eggs to treat one patient with therapeutic cloning.Prenticeestimates that it would take 800 million donated human eggs (from women of childbearing age) to treat diabetics, just in the United States, with embryonic stem cells derived from therapeutic cloning.4At a current cost of about $2,000 for less than a dozen eggs, the cost of retrieving that many eggs alone makes therapeutic cloning, as a viable treatment option, impossible.

West admits that one of Advanced Cell Technologies' greatest challenges is procuring all of the human eggs they need for their research.He writes, "Everyday FedEX shipments of hundreds of healthy cow oocytes have arrived at our doorstep.They've cost, at most, a dollar a piece. Human oocytes [eggs] however, have been far more difficult to find."5

To make therapeutic cloning a viable treatment, scientists need to find an alternative source of eggs other than women of childbearing age willing to go through invasive procedures.West has hinted at his answer.Jose Cibelli, a researcher at Advanced Cell Technologies, has already cloned his own DNA into cow eggs. (One wonders whether the American public would accept the idea of cloning humans using cow eggs.)

Alternatively, researchers are looking to harvest eggs from aborted fetuses.All of a woman's eggs come to be during her fetal development.A 20-week-old female has about 7 million eggs, the most she will ever have.Lori Andrews, a reproductive rights lawyer, makes the connection: "With over a million abortions a year, some scientists have begun to think the unthinkable: using female fetuses as a source of eggs".6

Finally, therapeutic cloning is currently not a viable treatment option because ESCs are nowhere near providing treatments for disease.Prentice writes, "Thus far, there is only scant evidence that embryonic stem cells can actually work in the body to successfully treat degenerative diseases.There are no current treatments available for human patients."7Before therapeutic cloning can become a medical option, several hurdles need to be over come. One of the major obstacles is that ESCs may be too undifferentiated.Stem cells take cues from surrounding cells and differentiate accordingly.ESCs belong in an embryo; they are meant for rapid generation of a human being, not for repairing damaged tissues.When they are removed from the embryo, they tend to get confused.Prentice explains, "...when taken out of that normal environment and placed into a lab culture dish, the ESCs do not behave as expected".The cells usually form a mixture of several different specialized cell types, along with some cells that just continue to grow.And it is these cells that continue to grow and divide that are potentially another big problem: if injected into a patient, they might form a tumor."8In animal studies, injected ESCs tend to form tumors and a mixture of cell types, not just the ones needed.In a study with rats, a little over half of them died from tumors resulting from injecting ESCs into their brains.9The fact that ESCs tend to form tumors is a huge problem to overcome.It requires the knowledge of how and which genes are turned on and off, at the right time, to produce the desired cell type.Researchers are far from understanding those processes.

There are ethical alternatives to therapeutic cloning.Adult stem cells show great promise in curing disease, without the need for cloning.(For more on adult stem cells, see the Stem Cell Research topic.) So why are advocates pushing Congress and President Bush to fund therapeutic cloning research?In my opinion, the ultimate end for therapeutic cloning is not to provide cures, but to pave the way for reproductive cloning, cloning to produce children. Gregory Pence, a bioethicist and cloning advocate, is correct when he writes, "Scientists are naive to think they can ban reproductive cloning and go ahead and study embryonic [therapeutic] cloning."10Many scientists are giddy with the possibilities of reproductive cloning and the genetic engineering of clones.(For more on genetic engineering, see the Genetics topic.)And while Congress debates the legality of SCNT in humans and remains distracted by the "hype" surrounding therapeutic cloning, scientists have free reign to develop SCNT in humans for any purpose. Also, I believe we have entered a cultural time where human embryos have become, not a precious gift of human life, but a commodity that many researchers cannot wait to exploit, regardless of whether cures will result or not.They want to divert precious research dollars toward the manipulation and destruction of human life, not toward research that actually shows real promise.It is crucial that, as a society, we recognize that therapeutic cloning is not the answer to cure devastating disease.